The UN human rights chief says more than 6,000 people have been killed in the conflict in eastern Ukraine since it erupted in April 2014.

In a statement on March 2, UN High Commissioner for Human Rights Zeid Raad al-Hussein decried the "merciless devastation of civilian lives and infrastructure" in the war between government forces and Russian-backed separatists who hold parts of the Donetsk and Luhansk provinces.

"More than 6,000 lives have now been lost in less than a year due to the fighting in eastern Ukraine," he said.

The Geneva-based UN rights body said that hundreds of civilians and military personnel were killed in recent weeks alone, after an upswing in fighting particularly near the Donetsk airport and the town of Debaltseve.

Moscow denies involvement, but the UN said that "credible reports indicate a continuing flow of heavy weaponry and foreign fighters" from Russia to the separatists since December.

A sharp decrease in fighting since the rebels seized Debaltseve in mid-February has raised hopes a February 12 cease-fire deal brokered by Germany and France could hold.